Fix data race detected by TSAN.
Fix data race detected by TSAN.

audiokit/AudioKit,audiokit/AudioKit,adamnemecek/AudioKit,adamnemecek/AudioKit,eljeff/AudioKit,audiokit/AudioKit,eljeff/AudioKit,eljeff/AudioKit,eljeff/AudioKit,adamnemecek/AudioKit,adamnemecek/AudioKit,audiokit/AudioKit